The present invention relates to a novel modified polymeric material, more particularly, perfluorocarbon-grafted polyurethanes having superior blood compatibility, and a process for their preparation. 2. Description of the Prior Art
In biomaterials to be contacted with blood, hydrophobic surfaces thereof exhibit inertness and lower interaction with aqueous solutions due to low surface free energy. In addition, biomaterials hardly absorb water so that their mechanical characteristics can be maintained in the entirety thereof.
It has been known that fluorine-containing compounds provide typically hydrophobic surfaces, the surface tension of which is lower than that of water, oil and other solvents. For these characteristics, fluorine-containing compounds have been employed in the technical field of surface treatment of fibers, such as water-proofing treatment, oil/water repelling treatment, and others [M. Hayek, "Encyclopedia of Chem. Tech." Vol. 24, p.442 (I984)]. A representative copolymer is the one of acrylic or methacrylic esters containing fluoroalkyl chains such as Scotchgard (commercially available from The 3M Company) and Zepel (commercially available from E. I. Du Pont De Nemours and Company). The maximum water-repelling property can be obtained when the number of carbon atoms constituting the fluoroalkyl chains is 6-8. It is believed that this water repelling property attributes to the exposed CF.sub.3 groups present in the fluoroalkyl chains which outwardly extend from the surfaces of the copolymers.
Particularly, fluorocarbon polymers have been used as medical materials, such as artificial blood vessels. The representative example includes an expanded polytetrafluoroethylene which is being sold under the tradename "Gore-Tex."
A number of studies have heretofore been made on polymeric materials having a hydrophobic surface by utilizing fluorine-containing compounds in order to enhance antithrombogenicity.
For example, Ito et al. reported that in L-glutamate copolymers containing a fluoroalkyl group, blood coagulation is decreased and interaction of the surface of the copolymers with blood components, including plasma proteins, platelets, and blood coagulation factors, is considerably suppressed, with the increase in the fluorine content of the copolymers [Int. J. Biol, Macromol., 10, pp 201-208 (1988)].
On the other hand, a number of studies, in which fluorine-containing compounds are used in place of conventional diisocyanates, polyols or chain extenders, have been made in attempt to improve further blood compatibility of the polyurethanes.
For example, Takakura, et al. have used a fluorinated diisocyanate in place of diphenylmethane diisocyanate (MDI) [2nd SPSJ Int. Polym. Conf., p.46 (1986)]. Zdrahala, et al. have used fluorinated glycols having a molecular weight of 1,600 in place of polytetramethylene glycol (PTMG) [3rd World Biomat. Congress, p.425 (1988)]. Also, Ratner has employed a fluorinated chain extender for the synthesis of polyurethane [Polymer in Medicine III, p.87 (1988)]. Ito, et al. [Artificial Heart II, p.35 (1987)] and Takakura, et al. [IUPAC Int. Symp. p.314 (1989)] have used fluorine-containing compounds in synthesizing polyurethanes.
The fluorine-containing polyurethynes synthesized according to these conventional methods exhibit a relatively increased blood compatibility and suppressed interaction with blood attributing to the hydrophobic surfaces of the polyurethanes and the strong electronegative effect of the fluorine atom. However, these conventional methods suffer from the defects that the mechanical properties of polyurethanes deteriorate during the synthesis of fluorinated polyurethanes. Moreover, the blood compatibility of the fluorine-containing polyurethanes thus obtained is insufficient to use them as biomaterials.